Membrane proteins comprise ~35% of proteome and imparts essential functionality to the cellular membrane. Compared to soluble proteins, the biogenesis of membrane proteins poses enormous challenges to cells, as these hydrophobic proteins are highly prone to aggregation and misfolding in aqueous cellular environments before arrival at their membrane destination. Our general goal is to understand how molecular chaperones overcome these challenges and ensure the proper biogenesis of membrane proteins. Our specific goal is to decipher the mechanism of a novel chaperone, cpSRP43, which ensures the targeted delivery of the most abundant membrane proteins on earth - the Light Harvesting Complex protein (LHCP) family. To this end, we will decipher the mechanism by which cpSRP43 protects the highly hydrophobic LHCPs from aggregation. We will elucidate how conformational flexibility in this chaperone enables it to coordinate its actions with the protein targeting and translocation machineries, and thus achieve the effective capture of membrane protein substrates in the aqueous phase as well as the efficient release of substrates at the target membrane. Finally, we will test whether cpSRP43 can chaperone engineered membrane protein substrates, and whether this activity allows it to improve the expression, localization, or stability of membrane proteins in vivo. Ultimately, these studies will allow us to better understand the intimate link between chaperone activity and membrane protein biogenesis, and provide a precedent for the mechanisms by which ATP-independent molecular chaperones using binding interactions to drive vectorial processes during protein localization. Exploiting the robustness and modularity of cpSRP43's activity could also lead to new and general tools to improve the production and behavior of membrane proteins.